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7. A molecular modelling analysis of why DDT and its
metabolites have prolonged persistence in the environment and the
living systems
Fazlul Huq
School of Biomedical Sciences,
Faculty of Health Sciences, C42, The University of Sydney, PO Box 170,
Lidcombe, NSW 1825, Australia.
f.huq@fhs.usyd.edu.au.
(Received 19 December 2005;
accepted 21 January 2006)
Abstract:
DDT is an organochlorine insecticide that has been extremely popular
because of its low cost, broad spectrum of insecticidal activity, ease
of application and stability in the environment. Even though the use
of DDT has been banned in many countries because of its toxicity to
wild life, it is still widely used in several parts of the world
including India
to control malaria, typhoid and
dengue vectors. Being chemically stable and insoluble in water but
soluble in fat, it accumulates in the living systems resulting into
biomagnification. DDT and a number of its metabolites also persist in
the environment. Molecular modelling analyses based on molecular
mechanics, semi-empirical (PM3) and DFT (at B3LYP/6-31G* level)
calculations show that generally it is the kinetic inertness rather
than thermodynamic stability that make DDT and its structurally
related metabolites resistant to change in the environment and living
systems. The longer half-life of DDE can however be explained in terms
of its greater thermodynamic stability as compared to DDT and DDD.
Key words:
DDT, DDE, DDD, toxicity, biomagnification, molecular modelling
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